Spatial coherence from Nd quantum emitters mediated by a plasmonic chain.

Controlling the coherence properties of rare earth emitters in solid-state platforms in the absence of an optical cavity is highly desirable for quantum light-matter interfaces and photonic networks. Here, we demonstrate the possibility of generating directional and spatially coherent light from Nd ions coupled to the longitudinal plasmonic mode of a chain of interacting Ag nanoparticles. The effect of the plasmonic chain on the Nd emission is analyzed by Fourier microscopy. The results reveal the presence of an interference pattern in which the Nd emission is enhanced at specific directions, as a distinctive signature of spatial coherence. Numerical simulations corroborate the need of near-field coherent coupling of the emitting ions with the plasmonic chain mode. The work provides fundamental insights for controlling the coherence properties of quantum emitters at room temperature and opens new avenues towards rare earth based nanoscale hybrid devices for quantum information or optical communication in nanocircuits.